A highly optimized conventional 193 nm-ArF photolithography system has a resolution limit of 52 nm. By contrast, the resolution limit for 193 nm immersion lithography in water is about 35 nm. This difference is motivating the search for solutions to the many practical issues of implementing immersion lithography.
As described by Y. Wei et al., Advances in Resist Technology and Processing XXIII, edited by Q. Lin, Proc. of SPIE Vol. 6153, 615306, (2006), topcoats are being developed to reduce the leaching of photoresist components into the immersion fluid, which is most often water. Another function of the topcoat is to provide a very hydrophobic surface to reduce water droplets or water mark defects. But the topcoat approach requires a separate step to apply the topcoat, and the topcoat must also be cleanly and completely removed after the post-exposure bake step to avoid the formation of blob defects.
WO2002021213 discloses resins and photoresist compositions that comprise such resins. The resins include photoacid-labile deblocking groups, wherein the acid-labile moiety is substituted with one or more electron-withdrawing groups, e.g., perfluoroalkyl groups. The polymers are useful as a resin binder component of chemically-amplified positive-acting resists that can be effectively imaged at wavelengths below 300 nm.
RAFT (reversible addition fragmentation chain transfer) polymerization processes have been disclosed for the preparation of low-polydispersity polymers from acrylic, styrenic and selected other vinyl monomers. (WO 98/01478, WO 99/31144, WO05031462B1, WO05031461A1, and EP 0 910,587). Fields of application for these RAFT-derived polymers include imaging and electronics (e.g., photoresists).
T.-Y Lee et al., (Advances in Resist Technology and Processing XX, Theodore H. Fedynyshyn, Editor, Proceedings of SPIE, Vol. 5039 (2003), pp 548-557) have disclosed the preparation of acrylate terpolymers using RAFT processes.
M. Mishra et al. have reviewed useful methods for the preparation of acrylate polymers (“Handbook of Radical Vinyl Polymerization”, Marcel Dekker, Inc., 1998).
There is a continuing need to develop photoresist compositions that display high contact angles with water and other immersion fluids.